If you take the bank of 8 it is like 2 banks of 4 @ 24 volts so you then multiply the amp hours of one member
of the bank of them by 2. You can combine the volts or the amp hours. So yes 550 amp hours would be the bank total rating at 24 volts.
Before you consider bigger replacements
consider how you will recharge the bank. your bank size is limited by your daily charging
capacity. You can charge it any way you like but you have to do it sometime regularly. A bank this size requires a fair amount of charging
. Have you tried to compute how much power you really need.
If you size the bank too large you won't be recharging it fully and so it will not last as long. Over time you only can use a bank as large as you can charge. If it is too small you'll be deeply discharging it and shortening it's lifespan as well. In both cases you'll be wasting a lot of money
. You really want the bank sized right. Replacement of the bank with Trojans is over $1,000 right now. All the cables
crimped with heat shrink tubing and other assortment of posts and breakers to set up the bank properly also costs a lot.
Better is getting the size just right.